Why stainless steel ?

There is very little difference between steel and iron. Pure iron is as soft as copper. By adding up to 2 percent carbon to it, incredible strength, hardness and mechanical properties are obtained, which is now called steel. The use of steel is also very common due to the abundance of iron and its easy and cheap availability. But steel also has a weak spot, which is in iron.

Rusting, in other words oxidation.

Every year, millions of dollars are wasted in the world as a result of the rusting of the items used in our daily lives. Most of this loss is due to rusting of iron and steel. We can briefly define rusting as the combination of iron with oxygen in the air. In fact, this is an electrochemical reaction. For this reason, rusting that starts in one part of the material can pass under the paint and appear in another place.

Not only iron and steel but also other metals rust. For example, aluminum, brass, bronze. However, in them, a very thin layer, consisting of the combination of the material and the oxygen, plays a protective role by cutting the contact of the material with the air as soon as it is formed, and prevents the progression of corrosion. This layer is so thin that the color of the material almost does not change. The characteristic of rust in iron is that there is no solid bonding on the surface due to the large difference in the sizes of its and oxygen atoms, the penetration of rust into the material, and deterioration of not only the appearance but also the strength.

Humidity in the air also has a great effect on rusting. The amount of water in the reaction also determines the color of the rust. Therefore, the color of rust can be black or very dark brown, or it can be yellowish. Another factor that increases the speed of rusting is salt. It also increases the rate of this electro-chemical reaction. In winter, places where salt is poured on the roads due to snow and on the seaside, rusting is faster.

Before stainless steel, the material was painted or galvanized to prevent rust. These solutions also created other problems, especially in the health and food sectors. Harry Brearley discovered the first stainless steel by accident in 1913. While experimenting with combining various metals for rifle barrels, he found that some were resistant to rust. As with every great invention, it took a long time to get it accepted by the industrialists.

Some metals, such as chromium, combine with oxygen very easily and rapidly due to their atomic sizes being close to each other. They form a very thin but very solid layer, only a few atoms thick. There is no other reaction. Even if this layer is damaged, it reappears. If chromium is added to the steel at a certain rate, the same thing happens, the steel will no longer rust. There is 10-30 percent chromium in stainless steel. Depending on this ratio and the nickel, titanium, aluminum, copper, sulphur, phosphorus and similar elements to be added, the places of use change.